The invention relates to a container, in particular a container with a tube-shaped wall made of a light metal alloy, for use as a reaction chamber in a process for manufacturing wafers, in particular for use in wafer-etching processes. The invention also relates to a process for its manufacture.
Such containers of a light metal alloy are known as inner containers for process containers for the treatment of wafers, in particular for performing wafer-etching processes.
Wafers are thin, oblate like discs less than 0.5 mm thick, which are cut out of single crystals of doped silicon or other semiconductor materials in order to be used for integrated printed circuits or the like electrical components. After removing ultra thin discs from a silicon ingot, these discs are lapped, etched and polished for wafer manufacture.
In contrast to lappingxe2x80x94in which rotating upper and underlying pads are used along with a crystalline granulate emulsion to remove material from the interlying silicon discxe2x80x94a grinding process removes larger amounts of material and achieves better surface quality; at the same time, the depth of damage to the crystal surface is less. By employing special grinding wheels and process parameters it is possible to create, high pressure and temperatures locally i.e. at the surface being worked and thus to plasticise the silicon; silicon fragments can be removed at the surface without causing the material to fracture.
Up to now, metal containers made from seamless tubes extruded over a mandrel have been employed for processing wafers of normal size i.e. 200 mm diameter. At a maximum tube diameter of about 450 mm this manner of producing the containers from an AIMg alloy containing about 4 wt. % Mgxe2x80x94i.e. an alloy with a high Mg content for adequate hardnessxe2x80x94is expensive. The inner surface is normally anodised. In spite of this the alloying elements have an effect on the wafer manufacturing process, in particular when, depending on the etching medium, defects are produced in the anodic layer or increase due to the attack of gases. Further, with increasing diameter of wafer, it is no longer possible to produce the desired design of container using the normal mandrel tool.
In view of the above the object of the present invention is to improve the ease of manufacture of such metal containers and to increase their service life.
In accordance with the invention the container wall is manufactured from a metallic material by extrusion, whereby the material employed has aluminum as its basis and a magnesium content between 1.2 and 2.0 wt. % along with an extremely low concentration of Cu, Fe, Sixe2x80x94approximately of the order of magnitude of impurities, i.e., less than 0.5%.
To advantage, for production of the tube, use is made of a cost-favourable special die, however,xe2x80x94instead of the AlMgSi alloy traditionally used with special diesxe2x80x94along with a new alloy for this purpose viz., the above mentioned AlMgx the fraction xe2x80x9cXxe2x80x9d of which, as said, lies between 1.2 and 2.0 wt. % and in particular contains no significant amount of Si, Cu or Fe.
Also within the scope of the invention is a container the wall of which along with a base plate is in the form of a single piece made from the above mentioned aluminum based material with a magnesium content between 1.2 and 2.0 wt. %.
By dispensing with a silicon content e.g. of 0.8 wt. % in the new processing a special die there is no longer the hardening effect which is to be expected by coagulation of intermetallic phases. Instead, an alternative hardening effect is achieved in that the magnesium content is increased. The prejudice prevalent among experts in the field viz., that large tubes can be produced only via a die when Mg and Si are present in the alloy was not found to hold.
A further possibility for manufacturing according to the invention is ring-type rolling of the container wall.
The result is that a tube with adequate weldability can be produced and has adequate strength for production of the container and for the described application, but does not contain Fe and Si which have an adverse effect on the wafer manufacture.